Gas turbine engine exhaust diffuser with movable struts

ABSTRACT

An exhaust diffuser for a gas turbine engine gas turbine engine includes a multiple of circumferentially spaced struts that extend between an inner gaspath wall and an outer gaspath wall, at least one of the multiple of circumferentially spaced struts movable about a strut axis.

BACKGROUND

The present disclosure relates generally to a gas turbine engine and,more particularly, to an exhaust diffuser of an auxiliary power unit(APU).

An auxiliary power unit (APU) is commonly installed in aircraft andvehicles to provide mechanical shaft power for electrical and hydraulicequipment such as electrical power generators, alternators and hydraulicpumps. APUs, much like other gas turbine engines, produce a certainamount of noise during operation. Typical noise reduction systemsinclude baffle mufflers and Herschel Quincke tubes, however, noisereduction and pressure recovery may often be a design challenge.

SUMMARY

An exhaust diffuser for a gas turbine engine according to one disclosednon-limiting embodiment of the present disclosure includes an innergaspath wall, an outer gaspath wall and a multiple of circumferentiallyspaced struts that extend between said inner gaspath wall and said outergaspath wall, at least one of said multiple of circumferentially spacedstruts movable about a strut axis.

In a further embodiment of the foregoing embodiment, each one of themultiple of circumferentially spaced strut is movable about a respectivestrut axis.

In a further embodiment of any of the foregoing embodiments, the innergaspath wall is defined around an engine centerline axis.

In a further embodiment of any of the foregoing embodiments, the outergaspath wall is defined around an engine centerline axis.

In a further embodiment of any of the foregoing embodiments, the atleast one of said multiple of circumferentially spaced struts includes ashroud movable about a pivot tube mounted to said inner gaspath wall andsaid outer gaspath wall. In the alternative or additionally thereto, inthe foregoing embodiment the pivot tube is hollow.

In a further embodiment of any of the foregoing embodiments, the atleast one of said multiple of circumferentially spaced struts is movableover an approximate +/−twenty degree range.

A gas turbine engine according to another disclosed non-limitingembodiment of the present disclosure includes an exhaust diffuser thatdefines a gaspath, a multiple of circumferentially spaced struts thatextend across the gaspath, at least one of the multiple ofcircumferentially spaced struts movable about a strut axis.

In a further embodiment of the foregoing embodiment, each one of saidmultiple of circumferentially spaced strut is movable about a respectivestrut axis.

In a further embodiment of any of the foregoing embodiments, the gaspath is annular.

In a further embodiment of any of the foregoing embodiments, the exhaustdiffuser is downstream of a turbine section.

A method of operating a gas turbine engine according to anotherdisclosed non-limiting embodiment of the present disclosure includesmodulating an exhaust diffuser downstream of a turbine section.

In a further embodiment of the foregoing embodiment, the modulatingincludes moving at least one of a multiple of circumferentially spacedstruts that extend across a gaspath defined by said exhaust diffuser.

In a further embodiment of any of the foregoing embodiments, themodulating includes pivoting at least one of a multiple ofcircumferentially spaced struts that extend across a gaspath defined bythe exhaust diffuser.

In a further embodiment of any of the foregoing embodiments, themodulating includes moving a multiple of circumferentially spaced strutsthat extend across a gaspath defined by said exhaust diffuser.

In a further embodiment of any of the foregoing embodiments, themodulating includes pivoting a multiple of circumferentially spacedstruts that extend across a gaspath defined by said exhaust diffuser.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art fromthe following detailed description of the disclosed non-limitingembodiment. The drawings that accompany the detailed description can bebriefly described as follows:

FIG. 1 is a general schematic view of an exemplary gas turbine engineaccording to one non-limiting embodiment;

FIG. 2 is an expanded view of an exhaust diffuser of the gas turbineengine;

FIG. 3 is an expanded perspective view of a movable exhaust strut of theexhaust diffuser; and

FIG. 4 is an expanded sectional view of the movable exhaust strut of theexhaust diffuser taken along line 4-4 in FIG. 2 to illustrate an examplerange of movement.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as an Auxiliary Power Unit (APU),however various gas turbine engines such as turboshaft engines may alsobenefit herefrom. The gas turbine engine 20 is circumferentiallydisposed about an engine centerline A. The gas turbine engine 20generally includes a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. The fan section 22 drawsin ambient air through for compression in the compressor section 24. Thecompressed air is then mixed with fuel and ignited in the combustorsection 26 to generate an annular stream of hot combustion gases that isexpanded through the turbine section 28 to extract energy and drive thefan section 22 and the compressor section 24.

The gas turbine engine 20 further includes an exhaust diffuser 30 thatgenerally includes an inner gaspath wall 32, an outer gaspath wall 34and a multiple of circumferentially spaced struts 36 that extendstherebetween. The exhaust diffuser 30 defines an annular gaspath 38 forthe hot combustion gases downstream of the turbine section 28.

In the disclosed non-limiting embodiment, at least one of the multipleof circumferentially spaced struts 36 is movable about a strut axis P (amoveable strut 36′ of FIG. 2) that is transverse or perpendicular to theengine longitudinal axis A. Although only a single movable strut 36′will be described in detail, it should be appreciated that all or asubset of the multiple of circumferentially spaced struts 36 may bepivotable and thus generally equivalent to the moveable strut 36′described in detail herein.

With reference to FIG. 2, the movable strut 36′ generally includes apivot tube 40 and a shroud 42. The pivot tube 40 extends between theinner gaspath wall 32, and the outer gaspath wall 34 to provide arequired stiffness to support a rear bearing housing (not shown) and theexhaust diffuser 30. The pivot tube 40 may be hollow to provide aservices path across the gaspath for wires, conduits, fluids,scavenging, etc. In one disclosed non-limiting embodiment, the axis Pdefined by the pivot tube 40 may be located at approximately on-thirdchord the shroud 42.

The shroud 42 is a generally airfoil-shaped member that surrounds thepivot tube 40 and rotates therearound. The shroud 42 is defined by anouter airfoil wall surface 44 of FIG. 3 between a leading edge 46 and atrailing edge 48. The outer airfoil wall surface 44 defines a generallyconcave shaped portion to form a pressure side 50 and a generally convexshaped portion to four a suction side 52 (FIG. 3).The outer airfoil wallsurface 68 is typically shaped to generally axially straighten thecombustion gases discharged from the turbine section 28.

Hot combustion gases discharged from the turbine section 28 into theexhaust diffuser 30 have a residual velocity component in the tangentialdirection with respect to the engine axis A. The tangential velocitycomponent of the hot combustion gases may detract from the momentumincrease that produces a forward axial thrust in the gas turbine engine.The tangential velocity component of the flow is redirected axially bythe multiple of circumferentially spaced struts 36. That is, the shroud42 defines an airfoil profile that axially straightens the combustiongases flow.

In the exhaust diffuser 30 aft of the turbine section 28, the multipleof circumferentially spaced struts 36 axially straightens residualswirl. The amount of swirl may vary from one engine operating conditionto another such that in some conditions, the flow may be subject to flowseparation. Flow separation may effect efficiency and noise levels asthe hot combustion gases discharged from the turbine section 28 into theexhaust diffuser 30 the swirl angle may vary by as much as approximately+/−20 degrees at different conditions.

With reference to FIG. 4, the shroud 42 of each of the movable strut 36′is freely movable about the pivot tube 40. The shroud 42, in onenon-limiting embodiment, may be mechanically limited in pitch to, forexample, an approximate +/−twenty degree range. The movable struts 36′thereby passively adjust to the variable swirl angle of the hotcombustion gases discharged from the turbine section 28. In other words,movement of the movable struts 36′ freely changes an angle of attack inresponse to the aerodynamic forces applied to the shroud 42 to modulatethe exhaust diffuser 30 and thereby minimize or eliminate the otherwisepossible flow separation that may result from the variance of swirlangle. The reduction or elimination of flow separation increasesefficiency and reduces noise levels over a significantly greater rangeof conditions as compared to conventional fixed strut architectures.

It should be understood that relative positional terms such as“forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like arewith reference to the engine but should not be considered otherwiselimiting.

Although the different non-limiting embodiments have specificillustrated components, the embodiments of this invention are notlimited to those particular combinations. It is possible to use some ofthe components or features from any of the non-limiting embodiments incombination with features or components from any of the othernon-limiting embodiments.

It should be understood that like reference numerals identifycorresponding or similar elements throughout the several drawings. Itshould also be understood that although a particular componentarrangement is disclosed in the illustrated embodiment, otherarrangements will benefit herefrom.

Although the different non-limiting embodiments have specificillustrated components, the embodiments of this invention are notlimited to those particular combinations. It is possible to use some ofthe components or features from any of the non-limiting embodiments incombination with features or components from any of the othernon-limiting embodiments.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent disclosure.

The foregoing description is exemplary rather than defined by thelimitations within. Various non-limiting embodiments are disclosedherein, however, one of ordinary skill in the art would recognize thatvarious modifications and variations in light of the above teachingswill fall within the scope of the appended claims. It is therefore to beunderstood that within the scope of the appended claims, the disclosuremay be practiced other than as specifically described. For that reasonthe appended claims should be studied to determine true scope andcontent.

What is claimed is:
 1. An exhaust diffuser for a gas turbine enginecomprising: an inner gaspath wall; an outer gaspath wall; and a multipleof circumferentially spaced struts that extend between said innergaspath wall and said outer gaspath wall, at least one of said multipleof circumferentially spaced struts movable about a strut axis.
 2. Theexhaust diffuser as recited in claim 1, wherein each one of saidmultiple of circumferentially spaced strut is movable about a respectivestrut axis.
 3. The exhaust diffuser as recited in claim 1, wherein saidinner gaspath wall is defined around an engine centerline axis.
 4. Theexhaust diffuser as recited in claim 1, wherein said outer gaspath wallis defined around an engine centerline axis.
 5. The exhaust diffuser asrecited in claim 1, wherein said at least one of said multiple ofcircumferentially spaced struts includes a shroud movable about a pivottube mounted to said inner gaspath wall and said outer gaspath wall. 6.The exhaust diffuser as recited in claim 5, wherein said pivot tube ishollow.
 7. The exhaust diffuser as recited in claim 1, wherein said atleast one of said multiple of circumferentially spaced struts is movableover an approximate +/−twenty degree range.
 8. A gas turbine enginecomprising: an exhaust diffuser that defines a gaspath, a multiple ofcircumferentially spaced struts that extend across said gaspath, atleast one of said multiple of circumferentially spaced struts movableabout a strut axis.
 9. The gas turbine engine as recited in claim 8,wherein each one of said multiple of circumferentially spaced strut ismovable about a respective strut axis.
 10. The gas turbine engine asrecited in claim 8, wherein said gas path is annular.
 11. The gasturbine engine as recited in claim 8, wherein said exhaust diffuser isdownstream of a turbine section.
 12. A method of operating a gas turbineengine comprising: modulating an exhaust diffuser downstream of aturbine section.
 13. The method as recited in claim 12, wherein saidmodulating includes moving at least one of a multiple ofcircumferentially spaced struts that extend across a gaspath defined bysaid exhaust diffuser.
 14. The method as recited in claim 12, whereinsaid modulating includes pivoting at least one of a multiple ofcircumferentially spaced struts that extend across a gaspath defined bysaid exhaust diffuser.
 15. The method as recited in claim 12, whereinsaid modulating includes moving a multiple of circumferentially spacedstruts that extend across a gaspath defined by said exhaust diffuser.16. The method as recited in claim 12, wherein said modulating includespivoting a multiple of circumferentially spaced struts that extendacross a gaspath defined by said exhaust diffuser.